Threat to Columbia River

While recreational boaters are being blamed for the spread of non-native mussels across the United States, another potential source may have emerged. Researchers believe the quagga mussel scare now facing the Columbia River may be linked to a shipment of hatchery-reared trout in Nevada.

"Between April and May 2006, three shipments of trout to Wildhorse Reservoir in northwestern Nevada may have introduced quagga mussel veligers [larvae] to the Columbia River water system," said Steven Wells, research assistant in the Center for Lakes and Reservoirs at Portland State University.

According to allegations made by Wells, a Lake Mead hatchery run by the Nevada Department of Wildlife is the initial source for the larvae-infested water holding the trout in transport. "The trout were delivered and entered the reservoir at the state park boat ramp," Wells continued.

Wildhorse Reservoir is considered the headwaters of the Owyhee River which enters the Snake River and eventually joins the Columbia.

"When quagga mussels were discovered in Lake Mead in early 2007, we modified and stepped up our monitoring system to look at the entire water column for veligers. After we learned of the Wildhorse [incident], we quickly formed a plan to deal with this specific event. Our center has been involved in monitoring for mussels all over the West since before 2003."

The Center for Lakes and Reservoirs — in conjunction with Nevada wildlife officials, the Piute Tribe and representatives of the Columbia River basin — continue to perform extensive monitoring of Wildhorse Reservoir and all waters downstream. "We have analyzed a lot of plankton and collected a lot of substrate data over the past," said Wells. "As of yet, we haven't found any signs of mussels. It is important to understand that when a reservoir experiences an inoculation event, the chances of that inoculation surviving are rare. But if it happens, the population would have to grow and build before we could even detect it."

As each month passes without testing positive for mussels, officials are breathing a little easier. "Because we're looking for microscopic organisms in sediment substrate testing and plankton analysis, it is possible to produce false negatives, so we will continue to monitor the water well into the future."